This invention relates to the provision of electromagnetic interference and electrostatic discharge shielding of an electronic system.
Modern electronic systems equipment, such as for telecommunications purposes, is often constructed as modular circuit packs inserted into guide slots of mechanical card cages, or shelf units, for engagement with a backplane mounted to the shelf unit at the inward ends of the guide slots. The outward edge of each circuit card is fastened to a face plate assembly which holds a latch for releasably retaining the circuit card in the shelf unit. Although the circuit cards are relatively closely packed, there are still gaps between adjacent face plate assemblies. There are also gaps in the face plate assemblies to allow portions of the latches to pass therethrough. All of these gaps allow electromagnetic interference radiation to leak therethrough. In addition, the gaps allow electrostatic discharge to pass therethrough, possibly causing damage to circuit components mounted on the circuit cards. A need therefore exists to provide shielding against electromagnetic interference and electrostatic discharge for such electronic systems equipment.
It is known to provide such shielding by encasing the electronic components within a conductive housing. While this "closed door" approach is satisfactory, there exists a need to provide such shielding under "open door" conditions, for example where a door to the enclosure is open to allow access to the equipment for maintenance purposes.